Fortune of one of America's richest men down more than 25% in past 6 months as fertilizer, oil, chemical markets all collapsed. Still, sales at his Koch Industries topped $100 billion in 2008; company now America's second-largest private company. Father, Fred C. Koch (d. 1967), invented method of turning heavy oil into gasoline. Sons Charles, David, Frederick and William inherited Koch Industries after father's death. Charles and David bought out William and Frederick for $1.1 billion in 1983. Today company has stakes in pipelines, refineries, fertilizer, fibers and polymers, forest and consumer products, chemical technology. Employs 70,000 workers in 60 countries. Purchased Invista, maker of Lycra and Coolmax fabric, in 2004 for $4.2 billion. Dropped $21 billion on paper and building-supply vendor Georgia-Pacific the following year. Brothers each own 42%. David is executive vice president. Holds chemical engineering degrees from MIT; pledged $100 million to alma mater for cancer research last year. Pledged another $100 million to New York's Lincoln Center last July.